optimization heliostats layout

Dear Paul,

Here is my another simulation,
My initial values are : Tower height = 203.33m, Receiver height  = 20.41m, Receiver diameter = 17.67m.
After I optimized the layout of heliostats, New values are: Tower height = 133.816m, Receiver height  = 10.8271m, Receiver diameter = 7.88733m, Heliostats reflective area = 88060 m2 . I accepted the updates of this layout.

In the same file, based on this updated layout (The number of heliostats and tower height, receiver height etc are already changed), I choose to optimize the layout again: Then the value became: Tower height = 63.8577m, Receiver height  = 8.50437m, Receiver diameter = 4.89721m, Heliostats reflective area = 94613 m2 .

So in this case, the tower height and receiver geometry are quite different. Then if i optimize the layout based on a already optimized result, is this acceptable or I should only optimize it once?

Best regards,
Francesca

Thank you for your interest in using SolarPILOT.  Toanswer your question, SolarPILOT uses the COBYLA algorithm for its non-linear
optimization functionality.  The COBYLA algorithm typically finds a nearby
local minimum which has no guarantee of being the global optimal
solution.  This being said COBYLA works best when you provide it with
“good” initial guesses for variable values.  This may require back of
envelope calculations or initial sampling of the design space.  Be sure to check the optimized system to ensure that it meetscommon-sense criteria for a layout and does not substantially violate peak flux
requirements. Theoptimization wizard should be used as a tool for gaining information, and is
not to be understood as an exhaustive and infallible design optimizer!  I
hope this helps.